1. Field of the Invention
This invention relates to video color synthesizers and, more particularly, to apparatus and techniques for transforming black and white video signals to corresponding color signals, the transformed color signals containing operator-controlled localized area color components which supplement the overall color transformation of the video signal.
2. Description of the Prior Art
Video coloring apparatus and techniques, whereby black and white video signals are transformed into color video signals, have been available for some time. However, such prior art devices and techniques are based predominantly, if not solely, upon techniques for transformation of grey levels of the black and white signal into corresponding color signals. By this technique, the incoming black and white video signal is effectively digitized, with amplitudes which fall within a predetermined number of discrete levels on the white to black scale being assigned corresponding colors. However, this technique of color transformation, or color conversion, carries the basic deficiency that the signal which is being processed simply does not carry information corresponding to the color components. In making a direct transformation from black and white to color, as is done in the prior art, no new information is in fact added to the color converted signal. Thus, all signals within a given grey level range are transformed into the same corresponding color, whereas in fact such grey levels may originally have been produced from distinctly different colors having the same shades of brightness. For this reason, unless and until additional information is put into the composite signal it remains virtually impossible to perfect a straight color conversion from black and white to color. Typical of the product which results from prior art color converting techniques is the color picture where a certain portion of the overall picture is well optimized, but another portion or another feature stands out as being poorly converted. For example, in an outdoor scene, bright portions of the frame may have a very excellent color, while shady portions have a poor color. Likewise, it frequently occurs that the background of a frame may have very excellent color, whereas the face of an individual may be clearly untrue in its coloring. The problem is acute, inasmuch as if any one sensitive portion of the frame is poorly color converted, the viewer senses this immediately and records displeasure with the entire scene. Color viewing is very subjective, and generally the viewer is sensitive to the coloring of certain features in an area or areas of the overall picture, to the relative exclusion of others. If the coloring of such color sensitive areas can be fine tuned without affecting the remaining portions, a highly acceptable final picture is achieved.
There currently exists a very strong demand to obtain a satisfactory technique for color converting black and white TV recordings and films. There exist large libraries and quantities of film and TV recordings in their original black and white state. If such films, which can be converted to black and white video signals by conventional means, and other video recordings, were available in satisfactory color, their value would increase manyfold. However, prior attempts to provide such color conversion have simply not been commercially acceptable, either because the end product was not artistically acceptable or because the operation was too expensive. This is evidenced by the fact that large numbers of prior films and recordings which were made in black and white simply are not utilized by the TV networks which show virtually no programs which are not in color.